Desired properties of tissue, including softness, bulk, stretch and absorbency, are achieved during a papermaking process by subjecting a paper web to a creping cylinder, for example a steam-heated Yankee Dryer, and a doctor blade. Prior to this stage, a wet fiber web has been largely dewatered at the pressure roll nip, or by a through air dryer (TAD) process. The mechanical action of the doctor blade results in a disruption of the fiber-fiber bonds and a formation of a microfold structure within the sheet.
In order to develop the crepe, the paper web has to adhere to the surface of the creping cylinder. Applying an adhesive to the dryer provides the adhesion. Most common creping cylinder adhesives are synthetic polymers such as polyaminoamides, polyamides, polyamines, polyvinylamines, polyvinyl alcohols, polyvinyl acetates, polyacrylamides, polyvinylpyrrolidones and polyethers. Other natural and derivatized natural polymers may also be employed including starch, guar gum, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose and the like. Various low molecular weight compounds are used to modify the creping cylinder coating properties.
A superior creping cylinder coating should form a film that provides good adhesion for efficient creping, and is also uniform, durable and soft. Uniformity of the coating is critical not only for consistent creping that affects the quality of the produced sheet, but also for even coverage of the creping cylinder surface to prevent premature wear of the cylinder and the blade. Durability is a characteristic of how stable the coating is on the creping cylinder surface, particularly at the pressure roll nip. If the coating is easily washed off, it does not protect the creping cylinder and leads to excessive creping blade wear. A hard coating causes blade chatter, which results in blade wear and non-uniform creping. A soft, but durable coating is preferred.
Tissue manufacturers are constantly striving to improve operational efficiency and product quality. Operations continue to be faced with issues such as hard coating build-up, chatter, loss of adhesion, and non-uniform coatings as creping cylinder surface temperatures are increased and/or sheet moisture contents are decreased in order to obtain better sheet properties from the creping process. Thus, there is a need for additional modifying agents that improve the product application window with regard to the creping cylinder temperature and moisture conditions.